Sound waves are introduced to a medium by a vibration. For example, a vibrating guitar string forces surrounding air molecules to be compressed and expanded. This creates a pressure disturbance consisting of an alternating bands of compressions and rarefactions. The vibration travels from particle to particle through the medium, transporting energy as it moves.
The amount of energy which is transported past a given area of the medium per unit of time is known as the of the sound wave and is reported as
power
area
.

A) frequency
B) intensity
C) pitch
D) wavelength